There has recently been an increased interest in electrochenistry and electrochemical phenomena of polymeric systems. See, in this regard, U.S. Pat. Nos. 4,222,903 and 4,204,216-- Heeger et al. and 4,321,114 and 4,442,187-- MacDiarmid et al. which are directed to the electrochemistry of certain conjugated polymers having extended conjugation in at least one backbone chain thereof. Each of the foregoing are incorporated herein by reference.
In U.S. patent application Ser. No. 620,446 filed Jun. 14, 1984, assigned to the assignee of this invention and incorporated herein by reference, certain electrochemical systems employing polyanilines as electrodes materials are described. Each of these systems have aqueous or otherwise protic electrolytes. Work in that area prior to the foregoing invention did not meet with successful development of secondary batteries, fuel cells, or substantially reversible electrochemical methods, however.
Jozefowicz et al., have undertaken certain electrochemical studies of certain forms of polyaniline as an anode and cathode in aqueous solution. See, for example, French Patent No. 1,519,729; French Patent of Addition No. 94,536; U.K. Patent No. 1,216,549; "Direct Current Conductivity of Polyaniline Sulfates", M. Diromedoff, F. Hautiere-Cristofini, R. DeSurville, M. Jozefowicz, L-T. Yu and R. Buvet. J. Chim. Phys., Physicoshim. Biol., 68, 1055 (1971); "Continuous Current Conductivity of Macromolecular Materials", L-T. Yu, M. Jozefowicz, and R. Buvet, Chim. Macromol. 1, 469 (1970); "Polyaniline-Based Filmogenic Organic-Conductor Polymers", d. LaBarre and M. Jozefowicz, C. R. Acad. Sci., Ser. C, 269, 964 (1969); "Recently Discovered Properties of Semiconducting Polymers", M. Jozefowicz, L-T. Y, J. Perichon and R. Buvet. J. Polym. Sci., Part C, 22, 1187 (1967); "Electrochemical Properties of Polyaniline Sulfates", F. Cristofini, R. DeSurville and M. Jozefowicz, C. R. Acad. Sci., Ser. C, 268, 1346 (1969); "Electrochemical Cells Using Protolytic Organic Semiconductors", R. DeSurville, M. Jozefowicz, L-T. Yu, J. Perichon and R. Buvet, Electrochim. Acta, 13, 1451 (1968); "Oligomers and Polymers Produced by Oxidation of Aromatic Amines", R. DeSurville, M. Jozefowicz and R. Buvet, Ann. Chim. (Paris), 2, 5 (1967); "Experimental Study of the Direct Current Conductivity of Macromolecular Compounds", L-T. Yu, M. Borredon, M. Jozefowicz, G. Belorgey and R. Buvet, J. Polym. Sci., Polym. Symp., 16, 2931 (1967); "Conductivity and Chemical Properties of Oligomeric Polyanilines", M. Jozefowicz, L-T. Yu, G. Belorgey and R. Buvet, J. Polym. Sci., Polym. Symp., 16, 2934 (1967); "Products of the Catalytic Oxidation of Aromatic Amines", R. DeSurville, M. Jozefowicz and R. Buvet, Ann. Chim. (Paris), 2, 149 (1967); "Conductivity and Chemical Composition of Macromolecular Semiconductors", L-T. Yu and M. Jozefowicz, Rev. Gen. Electr., 75, 1014 (1966); "Relation Between the Chemical and Electrochemical Properties of Macromolecular Semiconductors", M. Jozefowicz and L-T. Yu, Rev. Gen. Electr., 75, 1008 (1966); "Preparation, Chemical Properties, and Electrical Conductivity of Poly-N-Alkylanilines in the Solid State", D. Muller and M. Jozefowicz, Bull. Soc. Chim. Fr., 4087 (1972). Jozefowicz et al. employed a reduced form and an oxidized form of polyaniline, neither of which was analyzed or characterized in any way as to their chemical composition, as the anode and cathode respectively in one normal sulphuric acid (pH-O). They observed that such an electrochemical cell could be charged and discharged for two consecutive cycles.
Repetition of the disclosures of Jozefowicz has shown that the methods of Jozefowicz do not lead to substantial reversibility of electrochemistry involving polyaniline or to electrochemical cells having sufficient reversibility as to provide practical utility for secondary battery use.
Several papers have been published describing the use of "polyaniline" as a cathode in rechargeable battery cells in conjunction with a lithium anode in non-aqueous electrolytes.
In "Electrochemical Study of Polyaniline in Aqueous and Organic Medium. Redox and Kinetic Properties", E. M. Genies, A. A. Syed and C. Tsintavis, Mol. Cryst. Liq. Cryst., 121, 181 (1985), polyaniline film was synthesized in concentrated (presumably aqueous) HF solution. Charge density and other properties were determined in the HF solution. It is stated that it was very important "that the process retains some acidity in the polymer. If the polymer is completely neutralized, it becomes almost electroinactive and an insultator. In organic solvent, the residual acidity of the PANI remains in the polymer."
In "Secondary Batteries Using Polyaniline", 24th Battery Symposium in Japan, Osaka, Japan, 1983, p. 197, A. Kitani, M. Kaya and K. Sasaki report on certain lithium/polyaniline battery structures. No final oxidizing potential or information leading to a knowledge of the degree of protonation of the polyaniline film used in the Li/LiClO.sub.4 propylene carbonate/polyaniline battery is given, however. It is only stated that a potential of 0.8 V (versus a standard calomel electrode) in a 1 M aniline/12 M HClO.sub.4 solution was used in synthesizing the polyaniline. It has now been determined that this potential, in the presence of aniline, produces a green film, not a blue-purple (highly oxidized) film of the type formed if no aniline is present. In the presence of aniline at this potential the polyaniline is constantly being synthesized. In the absence of aniline, the only electrochemical reaction is the more extensive oxidation of the polyaniline. Kitani et al. state that they washed the film with water. This would cause an unknown and uncontrolled amount of deprotonation of the polyaniline salt, depending on the washing conditions.
In "Studies on Organic Polymers Synthesized by Electrolytic Method (II) Secondary Battery Using Polyaniline", A. Kitani, Y. Hiromoto and K. Sasaki, 50th Meeting of the Electrochemical Society of Japan, 1983, p. 123, it is stated that polyaniline film was synthesized by repeated potential cycling between --0.2 V and 0.8 V (no reference electrode is reported) in 0.1 M aniline/0.2 M HClO.sub.4. No reference is made as to the final potential at which the film was oxidized before it was used in a Li/LiClO.sub.4 (PC)/polyaniline cell. Also no mention is made as to how the product was washed. A pellet of polyaniline which was electrochemically synthesized in a powder form at 1.2 V "was also tested". This was apparently used only in aqueous electrolytes.
"Polyaniline as the Positive Electrode of Storage Batteries", M. Kaya, A. Kitani and K. Sasaki, 51st Meeting of the Electrochemical Society of Japan, Fukuoka, Japan, Apr. 28, 1984, P. 847, deals only with polyaniline in aqueous electrolytes, although in Table I electrochemical properties of a cell employing a Li anode are reported for comparative purposes.
Studies in aqueous electrolytes are described in "Secondary Battery Using Polyaniline", A. Kitani, M. Kaya, and K. Sasaki, 51st Meeting of the Electrochemical Society of Japan, Fukuoka, Japan, Apr. 28, 1984, p. 847.